Symmetry Tests and Vortex Imaging in Unconventional Superconductors

这一个人研究人员奖将为一位教授提供支持，该项目将解决超导体系统中相位和相位相干性的作用。该项目的一个目标将是确定一系列奇异超导材料中序参数的对称性。约瑟夫森干涉测量实验有助于确定高温铜酸盐的对称性，它将被应用于其他几个被怀疑表现出非常规对称性的系统，包括重费米子超导体，它表现出两个不同的超导相变，有机超导体，据信是d波，以及某些Ruthenate超导体，被认为是p波，具有复序参数，对应于时间反转对称性被打破的状态。对这些材料的低温穿透深度的测量是对这些材料的补充，这是对超导序参数中节点的最敏感的测试。这些实验对于确定配对对称性至关重要，从而能够表征复杂超导体的热力学、电磁和输运性质，并为发现超导电性的微观机制指明了方向。第二组实验将应用扫描鱿鱼显微镜来研究超导薄膜和晶体中磁涡的分布和运动。需要解决的关键问题是非常规超导体中涡旋晶格的几何形状和涡核的结构，低温下涡旋的钉扎和磁通蠕变，以及图案化薄膜中涡旋的运动，包括阶梯和棘轮结构中涡流的不对称性。在这个项目中，扫描鱿鱼显微镜技术将取得几项重大进展：提高亚微米区域的空间分辨率，在稀释制冷机中实现超低温成像，以及开发能够直接测试涡旋相互作用和钉扎的超导体系统中单个涡旋的移动和定位方案。与该项目相关的是介绍已建立的超导器件物理研究生课程，以及开发一门新的纳米器件和探测器课程。这个个人研究人员奖将为一位教授提供支持，该项目将讨论超导体系统中相和相干性的作用。超导材料的特征是一个量，即序参数，它在很大程度上决定了它们的电子性质。除了任何单个的量，正是这种序参数的相位导致了超导体令人着迷的性质，并导致了超导电子器件的独特潜力和能力。最重要的两个进展是在铜酸盐超导体中发现了以强烈的相位各向异性为特征的非传统配对(与在普通超导体中观察到的各向同性序参数相反)，以及开发了新的磁场探测仪器，使直接成像磁畴和涡旋成为可能。该项目将在两个方向上取得进展：(1)将进行实验，以确定几种被怀疑为非常规的奇异超导材料的序参数对称性，包括重费米子超导体、有机超导体和Ruthenate超导体。将使用两种互补的方法：直接探测序参数位相各向异性的相敏干涉实验，配对对称性的最明确测试，以及低温磁穿透深度的测量，这可能是序参数量级探测器中最灵敏的。(2)扫描SQUID显微镜将用于研究超导薄膜和晶体中磁涡的分布和运动。该仪器用灵敏的DC SQUID探测器扫描样品表面，以高磁场和高空间分辨率绘制磁场分布图。该项目将为一些超导相电子学领域的研究生提供培训，超导相电子学是当前量子信息处理和计算的一个感兴趣的主题。与该项目相关的是介绍已建立的超导器件物理研究生课程，以及开发一门新的纳米器件和探测器课程。***

This individual investigator award will provide support to a professor for a project that will address the role of the phase and phase coherence in superconductor systems. One objective of the project will be to determine the symmetry of the order parameter in a series of exotic superconducting materials. Josephson interferometry experiments, instrumental in establishing the symmetry of the high temperature cuprates, will be applied to several other systems suspected to exhibit unconventional symmetry, including heavy fermion superconductors, which exhibit two distinct superconducting phases transitions, organic superconductors, believed to be d-wave, and certain ruthenate superconductors, thought to be p-wave with a complex order parameter that corresponds to a state with broken time-reversal symmetry. Supplementing these are measurements of the low temperature penetration depth in these materials, the most sensitive test of nodes in the superconducting order parameter. These experiments are crucial to identifying the pairing symmetry, thereby allowing characterization of the thermodynamic, electromagnetic, and transport properties of complex superconductors, and pointing the way to discovery of the microscopic mechanism responsible for the superconductivity. A second set of experiments will apply Scanning SQUID Microscopy to study the distribution and motion of magnetic vortices in superconducting films and crystals. Key problems to be addressed are the geometry of the vortex lattice and structure of the vortex core in unconventional superconductors, the pinning of vortices and flux creep at low temperatures, and the motion of vortices in patterned films including asymmetries in vortex flow in step and ratchet structures. In connection with this project, several significant advances of the Scanning SQUID Microscopy technique will be developed: enhancement of the spatial resolution into the submicron regime, implementation of imaging at ultralow temperatures in a dilution refrigerator, and development of schemes for moving and positioning individual vortices in superconductor systems that will enable direct tests of vortex interactions and pinning. Associated with this project will be the presentation of an established graduate level course in Superconductor Device Physics and the development of a new course in Nanoscale Devices and Probes. %%%This individual investigator award will provide support to a professor for a project that will address the role of the phase and phase coherence in superconductor systems. Superconducting materials are characterized by a quantity, the order parameter, which largely determines their electronic properties. More than any single quantity, it is the phase of this order parameter that is responsible for the fascinating properties of superconductors and leads to the unique potential and capabilities of superconductor electronic devices. Two of the most significant advances have been the identification of unconventional pairing in the cuprates superconductors that is characterized by a strong phase anisotropy (in contrast to the isotropic order parameter observed in ordinary superconductors), and the development of novel magnetic field detection instruments that make possible direct imaging of magnetic domains and vortices. This project will build on these advances in two directions: (1) Experiments will be carried out to determine the order parameter symmetry of several exotic superconducting materials that are suspected to be unconventional, including heavy fermion superconductors, organic superconductors, and ruthenate superconductors. Two complementary approaches will be used: phase-sensitive interferometry experiments which directly probe the anisotropy of the phase of the order parameter, the most definitive test of the pairing symmetry, and measurements of the low-temperature magnetic penetration depth, which is perhaps the most sensitive of the probe of the magnitude of the order parameter. (2) Scanning SQUID Microscopy will be used to study the distribution and motion of magnetic vortices in superconducting films and crystals. This instrument scans a sensitive dc SQUID detector over the surface of a sample to map out the magnetic field distribution with high magnetic field and spatial resolution. This project will provide training for a number of graduate research students in the field of superconducting phase electronics, an topic of current interest for quantum information processing and computing. Associated with this project will be the presentation of an established graduate level course in Superconductor Device Physics and the development of a new course in Nanoscale Devices and Probes. ***